Three alternaric acid-related compounds, viz., 10-deoxyalternaric acid 2, 10-deoxy-6,19-dihydroalternaric acid 3, and 10-deoxy-6,8,9,19-tetrahydroalternaric acid 4, have been isolated from Alternaric solani which is a causal fungus of early blight disease on potato and tomato. The structures and stereochemistries of these compounds have been determined by spectral studies and chemical correlations. The structure–activity relationships of alternaric acid 1 and plausible biosynthetic routes from these compounds to alternaric acid 1 are also discussed.